We are studying the cellular basis for behavioral flexibility. Simple rhythmic behaviors are generated within the central nervous system by limited neural networks called Central Pattern Generators (CPGs). In isolation, a CPG can produce a stereotyped motor pattern, but in vivo, it interacts with an extensive network of modulatory and sensory inputs that can significantly change the properties of the neurons and synapses in the network. As a consequence, a single anatomically defined network can be "sculpted" to produce a variety of related behaviors. A loss of modulatory input would severely limit the behavioral flexibility of the animal by limiting the number of modes in which the motor network can operate. The cellular mechanisms that cause this sculpting of neural networks are not well understood. We are studying how three monoamines, dopamine, serotonin and octopamine, modulate the 14-neuron pyloric network in the crustacean stomatogastric ganglion. Each amine can induce a unique motor pattern when applied to the pyloric network. Our goal is to follow the complete process of behavioral modulation in this system, from the state of the animal that activates the monoaminergic inputs, through the cellular and ionic mechanisms that amines use to modify the pyloric network's functional circuit, to the altered motor pattern that evokes the changed behavior. We will combine current clamp, voltage clamp, and calcium imaging studies to determine the ionic mechanisms by which each amine alters the intrinsic electrophysiological properties of the neurons and their synaptic interactions. We will study the effects of these amines on the intact network in a variety of different states, and on its interactions with related networks, and try to interpret these effects based on the cellular and synaptic actions of the amines. Finally, we will study the identified neurons that provide the serotonin to the pyloric network, and analyze the behavioral context that activates them. This work will contribute to our understanding of how changes in the properties of cells and synapses in the nervous system can lead to changes in behavior. By showing how modulatory input sculpts a crustacean motor network to produce many behaviors, our work will serve as a model for studies of behavioral flexibility in other invertebrates and vertebrates alike.